This grant application represents a request to continue studies on the structure, function, and regulation of the mitochondrial ATPase complex of rat liier. This enzyme system participates in both ATP synthesis and in ATP-dependent functions; it is comprised of 8-10 different polypeptide chains representing one of the most complex enzyme systems of animal cells; and it is thought to be regulated by a small ATPase inhibitor peptide. Work supported by Grant CA 10951 has resulted in: 1) The purification of the oligomycin-sensitive ATPase complex (OS-ATPase) of rat liver mitochondria (Biochem., 1976); 2) The purification, crystallization, and characterization of the F1-component of OS-ATPase (JBC, 1971; 1972; 1973; 1976; 1978a); 3) the initiation of single crystal x-ray analysis of F1 (JBC, 1978b); 4) The purification of a small ATPase inhibitor peptide of the rat liver OS-ATPase (JBC; In prep., 1978); 5) The characterization of a variety of tumor mitochondria with respect to their capacity to catalyze ATP synthesis and ATP hydrolysis (JBC, 1974); and 6) The demonstration that mitochondrially synthesized ATP is coupled directly to the formation of G1c-6-P in highly glycolytic cancer cells (PNAS, 1977). In future work, the OS-ATPase complex of rat liver will be studied in order to establish its membrane orientation, identify its nearest neighbors, and ascertain whether it can couple H ion translocation directly to ATP synthesis. The crystals of F1-ATPase will be defined in terms of subunit, amino acid, and nucleotide composition. The ATPase inhibitor peptide will be studied with respect to its interaction with F1-ATPase and its potential physiological role. With regard to mechanism, studies will be initiated to ascertain whether ATP synthesis and ATP-dependent functions are catalyzed by the same site, different sites, or overlapping sites on the OS-ATPase complex. Finally, studies on the bioenergetics of cancer cells will be continued with emphasis on the purification of the OS-ATPase complex. All aspects of the proposed research will yield new information both necessary and fundamental to our eventual understanding of the mechanism and control of ATP synthesis and ATP-dependent functions in normal and neoplastic tissues.